Effects of fluquinconazole and silthiofam, applied as seed treatments to single or consecutive crops of wheat, on take-all epidemic development and grain yields

Seed treatments containing fluquinconazole, silthiofam or a standard fungicide mixture with no activity against take‐all were compared in all combinations of sequences in successive second and third winter wheat crops in five field experiments and second to fourth crops in a sixth experiment. Compared with the standard treatment, silthiofam decreased take‐all more effectively than fluquinconazole when crops were sampled at tillering. In samples taken in summer, during grain filling, silthiofam often decreased the incidence of take‐all (percentage of plants with root symptoms) more than fluquinconazole, but fluquinconazole more effectively decreased the incidence of severe take‐all (percentage of plants with more than 75% of their root systems blackened). It is suggested that these differences are a consequence of more effective control of primary infection of roots by silthiofam and of secondary, root‐to‐root, infection by fluquinconazole. Silthiofam usually increased yield more than did fluquinconazole, perhaps as a consequence of better early protection during tiller and/or spikelet formation. Treatment with either of the fungicides affected epidemic development in the treated crop and in crops grown subsequently. In particular, decreased take‐all had the effect of delaying the year‐to‐year epidemic, so that nontreatment of a subsequent crop resulted in an upsurge in disease. Treatment with either take‐all fungicide of a crop grown after a treated crop was relatively effective if the epidemic in the comparable nontreated crop sequence was continuing to increase. It was, however, detrimental if the disease was approaching its peak in the first treated crop, particularly if a treated (fourth wheat) crop was being compared with a similar crop in a nontreated sequence in which take‐all decline had developed. These results provide a basis for recommendations for the use of seed treatment fungicides in sequences of wheat crops.     

Fungal Communities and Disease Symptoms on Stem Bases of Wheat and Barley and Effects of Seed Treatments Containing Fluquinconazole and Prochloraz

Three successive crops of winter wheat or barley were grown as second, third and fourth cereals. Communities of fungi on shoot bases, identified after isolation on agar media, were more diverse (determined by number of taxa identified) on wheat than on barley, and their diversity increased from year to year. Diversity was not affected by seed treatments containing fluquinconazole or prochloraz. Eyespot (caused by Tapesia spp.) and brown foot rot (caused by Fusarium spp. or Microdochium nivale ) increased from year to year. Eyespot, brown foot rot (after the first year) and sharp eyespot (which remained infrequent), assessed in summer (June), affected wheat more than barley. Eyespot severity was increased slightly on barley by treatments containing fluquinconazole, formulated with or without prochloraz, in the second year (third cereal), when it was also decreased slightly on wheat by fluquinconazole plus prochloraz, except in plots where the treatment had been applied for two successive years. The increases or decreases in eyespot in the second year were accompanied by, respectively, decreases or increases in the frequency of Idriella bolleyi where fluquinconazole was applied alone. Although the eyespot pathogen Tapesia yallundae (but not Tapesia acuformis ) is sensitive to fluquinconazole in vitro , seed treatment, applied principally to control take-all disease, is likely to have only a small effect against eyespot (or other stem-base diseases), and then only on wheat and when formulated with prochloraz.     

The potential of non-pathogenic Gaeumannomyces spp., occurring naturally or introduced into wheat crops or preceding crops, for controlling take-all in wheat

Take‐all disease (Gaeumannomyces graminis var. tritici) in wheat crops is known to be suppressed by naturally occurring antagonistic fungi, closely related to the pathogen, that infect grasses and cereals. This form of suppression was re‐investigated because of the changing importance and role of grass weeds and grass covers in arable farming. Natural populations of the competitive fungus Gaeumannomyces cylindrosporus, allowed to develop under rye‐grass, were more effective than artificially introduced populations in suppressing the development of take‐all in following wheat crops. To be effective, the antagonist needs to be present before the start of wheat cropping. Introducing G. cylindrosporus, but not G. graminis var. graminis (a potential antagonist that is faster growing), into a previous crop, or just after the previous crop, sometimes suppressed take‐all, but the effect was small. It is concluded that, for any future attempts at biocontrol by these fungi, they should be introduced into a preceding crop not susceptible to take‐all. Take‐all inoculum in the soil should be at a minimum and effective hosts of the take‐all pathogen must not be present as weeds or volunteers.     

Effects of sowing date and volunteers on the infectivity of soil infested with Gaeumannomyces graminis var. tritici and on take-all disease in successive crops of winter wheat

In a field experiment on winter wheat, take‐all on plants and the infectivity of the soil were studied in crop sequences with different combinations of sowing dates. Take‐all was negligible in the first wheat crop, but thereafter the mean disease intensity (measured using a take‐all rating, TAR, with a maximum of 300) was 108, 190, 118 and 251 in the second to fifth successive crops. In each growing season, the disease differed amongst sequences and built up more rapidly and was more intense on plants sown in mid‐September than on plants sown in mid‐October. In late‐sown plots, where volunteers had been present during the mid‐September to mid‐October period, take‐all reached an intensity intermediate between that in early‐sown plots and that in late‐sown plots that had been kept free of volunteers. Volunteers, therefore, partially offset the expected beneficial effect of decreased disease with later sowing. Differences in take‐all amongst sequences were most pronounced in the second wheat crop and early sowing of the previous wheat increased intensity of disease. In the following (third) crop, differences in disease intensity amongst sequences were smaller. Soil infectivity (measured by seedling bioassay after harvest) built up progressively from a low level after the first crop to peak after the third crop. In this build‐up phase, soil infectivity estimates were always numerically greater after harvest of early‐sown treatments than after later‐sown treatments, although never significant at P= 0.05. The greatest difference (P= 0.06) was recorded in October before sowing of the third crop, where the comparison was between soil after two previous early sowings and soil after two previous later sowings and control of volunteers. In the same autumn, presence of green cover (i.e. volunteers) was associated with a smaller loss of soil infectivity between harvest and later sowing than occurred in an absence of green cover. In 2^nd–4^th crops, where comparisons were available and mean TARs indicated moderate levels of take‐all, sowing later had no yield benefit, despite more take‐all and greater soil infectivity associated with early sowing. Important considerations for the management of crops at risk of take‐all are 1) choosing appropriate sowing dates to minimize take‐all or to encourage take‐all decline and 2) controlling volunteers and weed hosts where crops are sown late to minimise take‐all.     

Effects of break crops,and of wheat volunteers growing in break crops or in set‐aside or conservation covers,all following crops of winter wheat,on the development of take‐all (Gaeumannomyces graminis var. tritici) in succeeding crops of winter wheat

Experiments on the Rothamsted and Woburn Experimental Farms studied the effects on take‐all of different break crops and of set‐aside/conservation covers that interrupted sequences of winter wheat. There was no evidence for different effects on take‐all of the break crops per se but the presence of volunteers, in crops of oilseed rape, increased the amounts of take‐all in the following wheat. Severity of take‐all was closely related to the numbers of volunteers in the preceding break crops and covers, and was affected by the date of their destruction. Early destruction of set‐aside/conservation covers was usually effective in preventing damaging take‐all in the following wheat except, sometimes, when populations of volunteers were very large. The experiments were not designed to test the effects of sowing dates but different amounts of take‐all in the first wheats after breaks or covers apparently affected the severity of take‐all in the following (second) wheats only where the latter were relatively late sown. In earlier‐sown second wheats, take‐all was consistently severe and unrelated to the severity of the disease in the preceding (first) wheats. Results from two very simple experiments suggested that substituting set‐aside/conservation covers for winter wheat, for 1 year only, did not seriously interfere with the development of take‐all disease or with the development or maintenance of take‐all decline (TAD). With further research, it might be possible for growers wishing to exploit TAD to incorporate set‐aside/conservation covers into their cropping strategies, and especially to avoid the worst effects of the disease on grain yield during the early stages of epidemics.     

Cover crops and compost prevent weed seed bank buildup in herbicide‐free wheat–potato rotations under conservation tillage

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Control of silver scurf (Helminthosporium solani) disease of potato with benomyl and thiabendazole

Benomyl and thiabendazole, applied as dusts to seed potatoes before chitting (sprouting), reduced the incidence of silver scurf disease on the progeny at lifting and during subsequent storage. Treatment of seed tubers 4 months prior to planting almost completely suppressed sporulation during storage, even under conditions very favourable for the growth of the fungus. The fungicides appeared not to act systemically because developing tubers grown from treated seed were just as susceptible to infection after inoculation as those from untreated. Control was due to effective inhibition of sporulation on the surface of diseased seed tubers after planting. There was no reduction in the amount of disease in subsequent generations of potato crops without further fungicidal treatment. Seed virtually free from silver scurf, produced from seed treated with fungicide in the previous year, yielded progeny with as much disease as progeny from untreated seed stocks.     

Grain yield and incidence of take-all (Ophiobolus graminis Sacc.) in wheat grown in different crop sequences

The yield of wheat and the incidence of take-all were measured in crops grown in six different 4-year sequences, repeated in 3 successive years. The first crop of winter wheat grown after oats or beans yielded 13–23 cwt/acre (1632–2887 kg/ha) more grain than wheat after wheat or barley. Spring wheat after oats yielded 2–5 cwt/acre (250–625 kg/ha) more than spring wheat after wheat. The smaller yields of wheat after wheat or barley were caused mostly by greater prevalence of take-all. Regression analysis indicates that each 1 % increase in straws with take-all decreased yield of winter wheat by 0·6%. Take-all was more prevalent in the second and third successive wheat crops after oats than in the fourth crop.     

The role of chitinese of Serratia marcescens in controlling the production of zearalenone by Fusarium graminearum

An experiment was designed to determine the role of the chitinase of S. marcescens in controlling the production of zearalenone by F. graminearum isolated from diseased wheat plants. Fusarium graminearum, F. avenaceum, F. equiseti, F. culmorum, and F. solani were isolated from diseased wheat plant. F. graminearum culture materials were highly pathogenic for wheat seedlings, toxic to ducklings and produced high levels of zearalenone. S. marcescens was grown on the cell wall of F. graminearum and its components, chitin and laminarin as a sole carbon source. The release of N-acetyl-D-glucosamine from chitin, F. graminearum cell wall and living or drying mycelium indicated substrate degradation. S. marcescens applied to F. graminearum infested wheat kernels decreased greatly the occurrence of zearalenone after 4 weeks of incubation. F. graminearum culture materials treated with S. marcescens proved to be non-toxic to ducklings and wheat seed germination.     

Induction of Systemic Resistance by Bacillus cereus Against Tomato Foliar Diseases Under Field Conditions

The ability of a rhizobacterium to protect tomato plants against naturally occurring diseases as well as to improve crop yield under field conditions was studied. The rhizobacterium was introduced to the plants through seed microbiolization. Treatments consisted of different frequencies of fungicide (Chlorothalonyl) sprayings (5, 10 or 20 applications) of tomato plants grown from either microbiolized or non‐microbiolized seeds over a 90‐day evaluation period. Treatment of non‐microbiolized seeds without fungicide application was included as a control. The progress of the following three naturally occurring diseases was evaluated in the field and quantified: early blight (Alternaria solani), late blight (Phytophthora infestans), and septoria leaf spot (Septoria lycopersici). All treatments resulted in reduced disease severity when compared with the control treatment. Highest final fruit yields were found after treatment of plants grown from non‐microbiolized seeds and sprayed with fungicide 20 times over 90 days, and for treatment of plants from microbiolized seeds that received 10 fungicide spray applications, although all treatments increased yield over that obtained in the control treatment. The results demonstrate that combined rhizobacterial and chemical treatments in the field may permit reducing fungicidal spraying frequency while at the same time increasing crop yields.     

Phosphorus benefits of different legume crops to subsequent wheat grown in different soils of Western Australia

Certain legume crops, including white lupin (Lupinus albus L.), mobilise soil-bound phosphorus (P) through root exudates. The changes in the rhizosphere enhance P availability to these crops, and possibly to subsequent crops growing in the same soil. We conducted a pot experiment to compare phosphorus acquisition of three legume species with that of wheat, and to determine whether the legume crops influence growth and P uptake of a subsequent wheat crop. Field pea (Pisum sativum L.), faba bean (Vicia faba L.), white lupin (Lupinus albus L.) and wheat (Triticum aestivum L.) were grown in three different soils to which we added no or 20 mg P kg^–1 soil (P0, P20). Growth, P content and rhizosphere carboxylates varied significantly amongst crops, soils and P levels. Total P content of the plants was increased with applied phosphorus. Phosphorus content of faba bean was 3.9 and 8.8 mg/pot, at P0 and P20, respectively, which was about double that of all other species at the respective P levels. Field pea and white lupin had large amounts of rhizosphere carboxylates, whereas wheat and faba bean had negligible amounts in all three soils at both P levels. Wheat grew better after legumes than after wheat in all three soils. The effect of the previous plant species was greater when these previous species had received P fertiliser. All the legumes increased plant biomass of subsequent wheat significantly over the unplanted pots in all the soils. Faba bean was unparalleled in promoting subsequent wheat growth on all fertilised soils. This experiment clearly demonstrated a residual benefit of the legume crops on the growth of the subsequent wheat crop due to enhanced P uptake. Faba bean appeared to be a suitable P-mobilising legume crop plant for use in rotations with wheat.     

The fate of residual 15N-labelled fertilizer in arable soils: its availability to subsequent crops and retention in soil

An earlier paper (Macdonald et al., 1997; J. Agric. Sci. (Cambridge) 129, 125) presented data from a series of field experiments in which ¹⁵N-labelled fertilizers were applied in spring to winter wheat, winter oilseed rape, potatoes, sugar beet and spring beans grown on four different soils in SE England. Part of this N was retained in the soil and some remained in crop residues on the soil surface when the crop was harvested. In all cases the majority of this labelled N remained in organic form. In the present paper we describe experiments designed to follow the fate of this `residual' <sup>15</sup>N over the next 2 years (termed the first and second residual years) and measure its value to subsequent cereal crops. Averaging over all of the initial crops and soils, 6.3% of this `residual' ¹⁵N was taken up during the first residual year when the following crop was winter wheat and significantly less (5.5%) if it was spring barley. In the second year after the original application, a further 2.1% was recovered, this time by winter barley. Labelled N remaining after potatoes and sugar beet was more available to the first residual crop than that remaining after oilseed rape or winter wheat. By the second residual year, this difference had almost disappeared. The availability to subsequent crops of the labelled N remaining in or on the soil at harvest of the application year decreased in the order: silty clay loam>sandy loam>chalky loam>heavy clay. In most cases, only a small proportion of the residual fertilizer N available for plant uptake was recovered by the subsequent crop, indicating poor synchrony between the mineralization of ¹⁵N-labelled organic residues and crop N uptake. Averaging over all soils and crops, 22% of the labelled N applied as fertilizer was lost (i.e., unaccounted for in harvested crop and soil to a depth of 100 cm) by harvest in the year of application, rising to 34% at harvest of the first residual year and to 35% in the second residual year. In the first residual year, losses of labelled N were much greater after spring beans than after any of the other crops.     

Arbuscular mycorrhizae in wheat and field pea crops on a low P soil: increased Zn-uptake but no increase in P-uptake or yield

Few field studies have investigated the contribution of arbuscular mycorrhizal fungi (AMF) to agricultural systems. In this study, the role of AMF in nutrition and yield of dryland autumn-sown wheat and field pea was examined through a 2-year crop sequence experiment on a red loam (Kandosol) in SE Australia. The soil was P-deficient and had low levels of root pathogens. In Year 1, levels of AMF were increased by growing subterranean clover or Linola^TM and decreased by growing canola or through maintenance of bare fallow with herbicides or tillage. In Year 2, hosts of AMF (wheat and field pea) and non-mycorrhizal canola were grown with 0 P or 20 kg ha^–1 of P as superphosphate. Yields of all Year 2 crops were increased by P-fertiliser. Year 1 treatment led to 2–3 fold variation in colonisation by AMF at each P-level for Year 2 wheat and field pea. High colonisation did not correspond with greater crop growth, yield, or uptake of P, K, Ca, Cu or S in wheat or field pea. However, total crop Zn-uptake and grain Zn concentration were positively correlated with colonisation by AMF, due to enhanced Zn-uptake after anthesis. For wheat, high colonisation also corresponded with reduced Mn-uptake and lower grain Mn concentrations. In a glasshouse experiment using a second P-deficient Kandosol, inoculation of wheat with Glomus intraradices and Scutellospora calospora enhanced uptake of Zn and P when no P-fertiliser was applied. We conclude that high colonisation by AMF is unimportant for productivity of the major field crops grown on the Kandosol soils that occupy large areas of cropland in temperate SE Australia, even under P-limiting conditions. Investigation of the factors that control functioning of arbuscular mycorrhizae under field conditions, especially temperature, is required.     

Susceptibility to take‐all of cereal and grass species,and their effects on pathogen inoculum

Two field trials were conducted to investigate different herbage grasses and cereals for their susceptibility to the disease take‐all, for their impact on concentrations of the pathogen, Gaeumannomyces graminis var. tritici (Ggt), in soil and for their effect on development of take‐all in a subsequent wheat crop. In the herbage grass trial, Bromus willdenowii was highly susceptible to Ggt, produced the greatest post‐senescence Ggt concentrations in soil and highest incidence of take‐all in following wheat crop. Lolium perenne, Lolium multiflorum and Festuca arundinacea supported low Ggt soil concentrations and fallow the least. The relationship between susceptibility to Ggt and post‐senescence concentrations in soil differed between pasture grasses and cereals. In a trial in which Ggt was added to half the plots and where wheat, barley, triticale, rye or fallow were compared, the susceptibility of the cereals to take‐all was not clearly linked to post‐harvest soil Ggt concentrations. In particular, triticale and rye had low and negligible take‐all infection respectively, but greater post‐harvest soil Ggt concentrations than barley or wheat. This indicates that low Ggt concentrations on roots may build up during crop senescence on some cereals. Soil Ggt concentrations were greater following harvest in inoculated plots sown to cereals, but in the second year there was more take‐all in the previously non‐inoculated than inoculated plots. Thus, the grass and cereal species differed in susceptibility to take‐all, in their impact on Ggt multiplication and in associated take‐all severity in following wheat crop.     

Sowing date and phosphorus utilization by wheat

The uptake and utilization of phosphorus (P) by cereal crops is influenced by the growing period of the crop. In this article the effect of sowing date on the utilization of P by wheat crops grown in southern NSW is reviewed. Crops sown early in the accepted sowing period require smaller inputs of P fertilizer to reach the maximum yield but produce grain with a higher concentration of P than crops sown late in the sowing season. For later sowings a higher rate of applied P is required to achieve the yield potential but this is not associated with a high grain P concentration or a high rate of removal of P from the soil. If grain with a high P concentration is required as seed for subsequent crops, then sowing early, even with little or no applied P fertilizer, is preferable, although crops sown early in the season are likely to remove more P from the soil than the amount applied in fertilizer.     

The effect of iprodione on the seed-borne phase of Alternaria brassicicola

Alternaria brassicicola infection of Brassica oleracea seeds was effectively controlled by a dust application of iprodione (Rovral 50% w.P.). At 2.5 g a.i./kg the seed-borne fungus was usually eliminated from samples with up to 61.5% affected seeds (35.5% internally diseased) but higher levels of infection required increased doses for complete eradication of the fungus. The germination of healthy seeds, including samples from 7–yr-old stocks, on filter paper was unaffected by the treatment. However, the germination of diseased samples, particularly those internally infected with A. brassicicola, was improved. More seedlings emerged from iprodione treated than from untreated seeds in glasshouse soil but the differences were not significant. The application of gamma-hexachlorocyclohexane to iprodione treated seeds sown in soil did not adversely affect subsequent emergence or disease control. Disease control was maintained and germination was not affected by the treatment when treated infected seeds were stored for 2 yr at 10 °C, 50% r.h. In a field trial iprodione seed treatment reduced seedling infection in a cabbage crop grown from naturally diseased seeds (100% contaminated, 45.5% internally infected) from 5.6 to 0.04%.     

Field tests of bacteria and soil-applied fungicides as control agents for take-all in winter wheat

Putative biological and chemical treatments for controlling take-all were used in each of three consecutive years at two locations where winter wheat crops were grown in naturally-infested fields. The chemical treatments more often decreased take-all than the biological treatments, but no treatment consistently and significantly decreased take-all, nor did any cause a significant increase in yield. An isolate of Bacillus cereus var. mycoides and one of B. pumilis, applied as soil drenches in autumn or spring, or in the seed furrows, were usually ineffective. Of the few significant effects on disease, half were associated with increases and half with decreases, and most occurred in April and did not persist to late June. Two strains of Pseudomonas pluorescens applied to the seed were ineffective. The fungicide benomyl, applied as a drench in autumn and spring at 20 kg/ha was ineffective, while nuarimol, applied as a drench in autumn at 2 kg/ha was sometimes effective. Nuarimol incorporated into the seed bed at 2 kg/ha was the most effective treatment. In analyses using a functional relationship model for data from treated and untreated plots 12% of 176 data sets for biological treatments, 38% of 96 data sets for chemical treatments and 81% of 16 data sets for combined treatments showed increasing efficiency of the treatment with increasing disease intensity. These findings also demonstrate an additional advantage of the experimental design, namely that treatments are tested at different disease intensity levels within fields.     

Modelling wheat growth and yield losses from late epidemics of foliar diseases using loss of green leaf area per layer and pre-anthesis reserves

BACKGROUND AND AIMS: Crop protection strategies, based on preventing quantitative crop losses rather than pest outbreaks, are being developed as a promising way to reduce fungicide use. The Bastiaans' model was applied to winter wheat crops (Triticum aestivum) affected by leaf rust (Puccinia triticina) and Septoria tritici blotch (STB; Mycosphaerella graminicola) under a range of crop management conditions. This study examined (a) whether green leaf area per layer accurately accounts for growth loss; and (b) whether from growth loss it is possible to derive yield loss accurately and simply. Methods Over 5 years of field experiments, numerous green leaf area dynamics were analysed during the post-anthesis period on wheat crops using natural aerial epidemics of leaf rust and STB. Key Results When radiation use efficiency (RUE) was derived from bulk green leaf area index (GLAI), RUE(bulk) was hardly accurate and exhibited large variations among diseased wheat crops, thus extending outside the biological range. In contrast, when RUE was derived from GLAI loss per layer, RUE(layer) was a more accurate calculation and fell within the biological range. In one situation out of 13, no significant shift in the RUE(layer) of diseased crops vs. healthy crops was observed. A single linear relationship linked yield to post-anthesis accumulated growth for all treatments. Its slope, not different from 1, suggests that the allocation of post-anthesis photosynthates to grains was not affected by the late occurring diseases under study. The mobilization of pre-anthesis reserves completely accounted for the intercept value. Conclusions The results strongly suggest that a simple model based on green leaf area per layer and pre-anthesis reserves can predict both growth and yield of wheat suffering from late epidemics of foliar diseases over a range of crop practices. It could help in better understanding how crop structure and reserve management contribute to tolerance of wheat genotypes to leaf diseases.     

Late foliar diseases in wheat crops decrease nitrogen yield through N uptake rather than through variations in N remobilization

Background and Aims

French wheat grains may be of little value on world markets because they have low and highly variable grain protein concentrations (GPC). This nitrogen-yield to yield ratio depends on crop nitrogen (N) fertilization as well as on crop capacity to use N, which is known to vary with climate and disease severity. Here an examination is made of the respective roles that N remobilization and post-anthesis N uptake play in N yield variations; in particular, when wheat crops (Triticum aestivum) are affected by leaf rust (Puccinia triticina) and Septoria tritici blotch (teleomorph Mycosphaerella graminicola).

Methods

Data from a 4-year field experiment was used to analyse N yield variations in wheat crops grown either with a third or no late N fertilization. Natural aerial epidemics ensured a range of disease severity, and fungicide ensured disease-free control plots. The data set of Gooding et al. (2005, Journal of Agricultural Science 143: 503–518) was incorporated in order to enlarge the range of conditions.

Key Results

Post-anthesis N uptake accounted for a third of N yield whilst N remobilization accounted for two-thirds in all crops whether affected by diseases or not. However, variations in N yield were highly correlated with post-anthesis N uptake, more than with N remobilization, in diseased and also healthy crops. Furthermore, N remobilization did not significantly correlate with N yield in healthy crops. These findings matched data from studies using various wheat genotypes under various management and climatic conditions. Leaf area duration (LAD) accurately predicted N remobilization whether or not crops were diseased; in diseased crops, LAD also accurately predicted N uptake.

Conclusions

Under the experimental conditions, N yield variations were closely associated with post-anthesis N uptake in diseased but also in healthy crops. Understanding the respective roles of N uptake and N remobilization in the case of diseased and healthy crops holds the promise of better modelling of variations in N yield, and thus in GPC.Key words: Triticum aestivum, Puccinia triticina, leaf rust, Mycosphaerella graminicola, Septoria tritici blotch, N uptake, N remobilization, N yield, Leaf area duration     

Crop identity and memory effects on aboveground arthropods in a long‐term crop rotation experiment

Agricultural landscapes are globally dominated by monocultures under intensive management. This is one of the main reasons for biodiversity loss and insect population decline in many regions all over the world. Agroecosystem biodiversity in these areas can be enhanced by cropping system diversification, such as crop rotations. Yet, long‐term studies on effects of crop rotations on aboveground agrobiodiversity are lacking. We set up a 10‐year long‐term crop rotation experiment in Central Germany and monitored the temporal dynamics of aboveground arthropods over a full cultivation period to investigate influence of current and preceding crop identity and cropping system diversification on activity density, species richness, and community structure. We found that species composition was strongly influenced by currently grown crop although effect on arthropods varied between species groups. Especially, winter oilseed rape strongly affects arthropod community structure. Interestingly, we were also able to show an influence of the preceding crops, indicating an ecological memory effect in the aboveground arthropod community. Our results show that crop identity of both currently and previously grown crops in crop rotations may lead to an increase in arthropod activity density and changes in species composition. Diversified crop rotations including appropriate crops can be an easily implemented tool to increase arthropod biodiversity and biomass at large spatial and temporal scales, particularly in areas dominated by a single crop (e.g., wheat, maize). Our results may help to design optimized crop rotations for large‐scale enhancement of insect biodiversity in agroecosystems.